Job Control Language

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Job Control Language
Bhargava KC Extension 52067 ER Rotunda, II
Floor, Cubicle 15 Email bhargava_sastry_at_infy.com
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JOB CONTROL LANGUAGE For IBM Mainframe System
390
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Pre-requisites

• Programming Fundamentals.
• MVS Operating system and its subsystem TSO.
• Navigating through ISPF.

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Evaluation Scheme

• Quiz 20 Marks
• ( Conducted after 2 sessions of Input )
• OLE 80 Marks

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References
Title Authors
Publishers 1.
MVS JCL Doug Lowe
Mike Murarch and Associates 2.
System 370/390 JCL GD Brown 3.
IBM Manuals

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Objectives of the Course

• To acquaint participants to the specific nature
  of Job Control Language.
• To illustrate the syntax of JCL.
• To demonstrate the JCL programs, procedures,
  Various Data set allocation mechanisms, IBM
  Utilities
• To acquaint the participants regarding the
  importance of VSAM, GDGs, and concepts of SMS.

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Objectives of the Session

• To learn about JES as a Sub system and its
  functions.
• About JCL syntax in general
• About Job statement.
• Some sample examples.

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JOB AND A JCL

A JOB is the execution of one or more related
programs in sequence. Each Program to be
executed by a Job is Called a Step. Ex The
first program sorts customer names in a sequence
The second program generates a report
. Job Control Language is a set of control
statements that Provides specifications necessary
to process a Job.




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J
C
L
JOB
CONTROL
LANGUAGE
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JES interprets JCL and passes it to MVS
Determine the job
Create the JCL
Submit the JOB
MVS does the work
System Messages
JES collects the output and information about the
JOB
User Views and Interprets output
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WHY JCL ???

• MVS operating system is designed to work in the
  batch processing mode
• JCL is a powerful and flexible language that
  helps to customize the use of local and remote
  resources available to one or more computers

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Difference between batch interactive
processing

• Batch processing
• Jobs submitted are executed at later time
• User can not interact
• Performance measure is throughput
• Snapshot of output is used for debugging

• Interactive processing
• Jobs submitted are executed immediately
• User can interact
• Performance measure is response time
• Interactive debugging

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Various stages of JCL execution

• Input
• Conversion
• Execution
• Output
• Hard copy
• Purge

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Various stages of JCL execution

• Input JES gives a unique job number
• Conversion Check syntax error Place it in
  JES spool
• Initiator Taking the job from the spool
  and sending it for execution
• Output sends the output to printer
• Purge After job is processed,it is purged

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• Stages of Job Processing - INPUT

Job entry or input is how jobs are entered
into the system.
Several methods are

• Local and remote card readers

• Via a started procedure

• Internal reader

• From another system via network job entry

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Stages of Job Processing - INPUT

INPUT
MVS

SPOOL
JCL SYSIN
JES
During input processing , the job is placed out
on spool. At this point in time, a job consists
of

• Any JOB Control Language

• Any JOB Entry Control Language (JECL) in the
  Input Stream

• Any data SYSIN in the Input Stream

An entry is initialized in the Jobqueue and the
job is assigned a JES Job Number as part of
Input Processing
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Stages of Job Processing -CONVERSION
SPOOL
MVS
JCL SYSIN

JES
PROCLIB
PROC

• Input to the conversion process consists of the
  Original JCL and
• any cataloged procedure referenced by it

• Full Syntax checking of the JCL is done at this
  time

• During conversion the JCL for a job is converted
  to its internal
• form, known as Converter/Interpreter text. All
  of the jobs that
• were marked awaiting conversion in the job Queue
  are converted

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Stages of Job Processing -CONVERSION
JOB INTERPRETER - JES2

• JES2 gives job to idle initiator

PAY JCL
INTERPRETER

• Initiator attaches the interpreter
• to build control blocks

PAY CONTROL BLOCKS

• Control blocks used to start job
• in initiator

JES2 ADDRESS SPACE
INITIATOR ADDRESS SPACE
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Stages of Job Processing -CONVERSION
JOB INTERPRETER - JES3

• JES Attaches the interpreter

PAY JCL

• Interpreter builds the control
• blocks in the JES address space

INTERPRETER

• JES passes the CONTROL
• blocks to an idle initiator to
• start execution.

PAY CONTROL BLOCKS
JES3 ADDRESS SPACE
INITIATOR ADDRESS SPACE
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Stages of Job Processing - EXECUTION

• Initiator Invokes a program called Interpreter
  which goes thru the
• Job Input and creates a series of
  Control blocks in Scheduler
• Work Area , a part of Address space Private
  Area.
• 2. It then invokes Allocation routines that
  decides on what resources
• the Job step needs in terms of Units ,
  Volumes and Data sets.
• 3. Initiator then builds a User region where
  the Users program
• is loaded , control is transferred to
  Program and the program gets
• executed.
• When the Program execution is over Initiator
  invokes deallocation
• routines to release all the resources that
  are used.

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Stages of Job Processing - EXECUTION

• INITIATOR is responsible for the EXECUTION step
  of the Job

Initiator Eligible Job classes
1 A 2 B,C,D,H,L,T
3 B,C,D,H,L,T 4 B,C 5 B,C
6 C
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Stages of Job Processing - EXECUTION

• JES selects a job for execution , based upon job
  CLASS
• and job selection PRTY
• ex. //PAY JOB PRTY8,CLASSA

• Allocation ( of data sets and devices necessary
  for execution )
• is performed.

• If the program reads any SYSIN data, a copy
  will be read
• from Spool and presented to the program.

• If the program creates any SYSOUT data, it
  will be
• Spooled, rather than sent directly to an
  output device.

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Stages of Job Processing - OUTPUT

• After the job has terminated, the output created
  is
• analysed and grouped according to SYSOUT
• class and output characteristics

• Entries are then created in the Job Output Table
  
• (JOT) to reflect these various groupings

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Stages of Job Processing - HARDCOPY

• During this phase, job output characteristics
  and
• the output is sent to the physical devices.

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Stages of Job Processing - PURGE

• During Purge processing, all of the resources
  allocated
• to the job in earlier phases can be freed for
  re-use.
• These include

• Spool Space

• Jobqueue space

• JES job number

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JCL PROCESSING
INPUT STREAM
SPOOL
JES2 / JES3
JCL
SYSIN
SYSOUT
INITIATOR2
INITIATOR1
PRINTER
JES2 / JES3
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JCL execution
JCL INITIATION
STEP INITIATION
JCL
ALLOCATION
SYSIN
SYSOUT
PROGRAM EXECUTION
STEP TERMINATION
JOB TERMINATION
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QUESTIONS ???

• JCL is used to write an application program ?
• Yes/No

• What are the different stages of JCL processing ?

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JCL statements

• JOB Job identification
• EXEC Instruction for execution
• DD Source of data to operate

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TYPE OF STATEMENTS

• JOB CONTROL STATEMENTS
• UTILITY CONTROL STATEMENTS

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Basic Format of a JCL

• JCL statements are coded in 80 byte records -
• Only 72 of the 80 chars available to code JCL -
• last eight columns of each record reserved for an
  optional sequence number

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Basic Format of a JCL

• JCL FIELD NAMES
• Identifier field
• NAME field
• OPERATION field
• PARAMETER field
• Positional
• Keyword
• COMMENT field

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JCL STATEMENT FORMAT

• //P123 JOB 1234,AMLAN,CLASSE JOBSTATEMENT
• Name Parameters
• Operation
• Identifier Comment

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Basic Format of a JCL ...

• Identifier Name Operation Parameters
  Comments
• Identifier
• Two slashes ( // ) starting in col 1.
• Exceptions -
• 1) For a delimiter statement, / starting in col
  1
• 2) For a comment statement , // starting at col
  1
• Name
• One to eight alphanumeric , starting with a
  letter char. Starts from col 3. Valid chars
  A-Z,0-9 or national characters ( , _at_ , )

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Basic Format of a JCL ...

• Operation
• A valid operation code, such as JOB, EXEC or DD.
  Must be preceded and followed by a space.
• Parameters
• One or more parameters depending on the
  operation. Individual parameters are separated
  from one another by commas, no intervening
  spaces.
• Comments
• comments may follow parameters, preceded by one
  space and not extending beyond col 71

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JCL parameters

• JCL parameters
• 1) Positional parameters -
• Must occur at a specific position within the
  parameters field
• account for a missing parameter by a comma
• 2) Keyword parameters -
• UNITSYSDA ( no spaces )
• UNIT is a keyword parameter of value SYSDA
• Keyword parameters to come only after all
  positional parameters have been coded, order of
  keyword parameters immaterial

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JCL subparameters

• DCB(DSORGPO,LRECL80,BLKSIZE6160)
• DCB(DSORGPO) DCBDSORGPO
• DISP(,DELETE)

Comma place holders are required only for
missingpositional subparameters.
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Continuing JCL statements ...

• Break the parameter field with the comma that
  follows a parameter or sub-parameter
• Slashes in column 1 2 of following line
• Next parameter or sub parameter starting anywhere
  between columns 4 - 16

• //SYSUT2 DD DSNAME...,DISP...,//
  UNITSYSDA,VOLSERMPS800,//
  SPACE(CYL,(10,5,2)),// DCBDSORGPO

( X ) Avoid continuing comments from line to line.
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Guidelines

• JCL cryptic
• Code just one or two parameters per line
• align the operation and parameters fields of each
  statement
• begin job with a group of comment statements that
  document a job thoroughly
• Name, date of coding, what each job step does,
  any special processing requirements
• Dont forget to update comments !

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JCL statements

• JOB Job identification
• EXEC Instruction for execution
• DD Source of data to operate

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JOB STATEMENT

• ACCT CLASS
• NAME NOTIFY
• MSGLEVEL TYPRUN
• MSGCLASS PRTY
• COND RESTART
• USER REGION
• PASSWORD PERFORM
• TIME

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IMPORTANT JOB PARAMETERS
positional parameters ( a/c inf
),name
ex. //INFOSYSA JOB (A123),AMLAN

• All these parameters are optional as far as JCL
  is concerned,
• they are probably required by your installation.

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IMPORTANT JOB PARAMETERS keyword
parameters ( CLASS )
ex. //INFOSYSA JOB CLASSA

• CLASS specifies the job class that is the
  nature of the job.
• Installation will specify which of the 36
  possible classes to use
• which is from A to Z and 0 to 9 .

• Installation establishes a default class that is
  in effect if CLASS
• is omitted.

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IMPORTANT JOB PARAMETERS keyword
parameters ( MSGCLASS )
ex. //INFOSYSA JOB MSGCLASSA

• MSGCLASS specifies the job scheduler message
  output class.

• Job scheduler messages include all messages not
  printed by the
• job steps being executed but the JCL messages
  and system messages

• Installation establishes a default class that is
  in effect if CLASS
• is omitted.

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IMPORTANT JOB PARAMETERS keyword
parameters ( MSGLEVEL )
ex. //INFOSYSA JOB MSGLEVEL(1,1)

• MSGLEVEL(jcl,allocations) specifies the
  printing of JCL
• statements and allocation messages.

• ex. MSGLEVEL(0,1) will print only JOB statement,
  and
• all the allocation,JES,SMS and operator
  messages

• By default it is MSGLEVEL(1,1)

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keyword parameters ( MSGLEVEL )
MSGLEVEL(X,Y) Where X is 0 thru 2 , Y is 0
thru 1
X 0 , Lists Job statements only. X 1 , Lists
all User JCL All catalogued procedures. X 2
, Lists all User JCL but no catalogued
procedures. Y 0 , No Initiator/terminator
messages to be listed. Y 1 , All
initiator/terminator messages to be listed.
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IMPORTANT JOB PARAMETERS keyword
parameters ( NOTIFY )
ex. //INFOSYSA JOB NOTIFYINFOSYS

• NOTIFY notifies you at a time-sharing terminal
  when the job is
• completed.

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IMPORTANT JOB PARAMETERS keyword
parameters ( TYPRUN )
ex. //INFOSYSA JOB TYPRUNSCAN

• TYPRUN checks the JCL and holds the job in the
  input queue.

• TYPRUN SCAN checks the JCL for syntax errors
  and suppresses execution
• of the job

• TYPRUN HOLD holds the JCL in the input queue
  for later execution.It is held
• until the operator releases it.

• TYPRUN JCLHOLD(JES2 only) similar to HOLD but
  the difference is it is
• checked while it is not with the HOLD option.

• TYPRUN COPY(JES2 only) lists or duplicates the
  lines placed in the JOB
• statement to the class assigned in the
  MSGCLASS parameter and suppresses
• execution.

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SOME OTHER keyword JOB PARAMETERS

• PRTYpriority is related to the CLASS
  parameter. It assigns
• priority to jobs which belong to the same
  class.priority numbers
• range from (0-14) or (0-15) depending on
  installations.

• TIME(min,sec) signifies how much time the JOB
  must take to run.

• RESTARTSTEP3 Forces the JOB execution to start
  from STEP3.

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SOME OTHER keyword JOB PARAMETERS

• ADDRSPCREAL It is used to specify whether the
  program is
• to use REAL or VIRTual ADDRess SPaCe. Default
  is Virtual. If
• Real is coded then the REGION parameter is
  also to be coded.

• REGION96K To override the default amount of
  workspace
• assigned for the job.

• COND(4,LT) Permits the execution of a steps to
  depend on the
• return code from the previous steps.Will be
  dealt in detail in Day2.

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Errors

• JCL syntax errors.
• JOB will not be executed
• JCL allocation errors.
• JES2-subsequent steps will not get executed.
• JES3-detects errors in the beginning.

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Abend Failures
An ABEND failure occurs under the following
conditions A program while executing, attempts
to perform an instruction or operation which the
system recognizes as being impossible or
unacceptable.

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Causes of Abend Failures

• Logic error
• JCL error
• Resource unavailability
• Exceeding limits (Time or Space on DASD)
• Hardware Malfunction
• User ABENDS
• Operator intervention
• Operating System failure

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Thats all for DAY 1